Semiconductor photodiodes are well known and commercially available. Typically, such a photodiode has a PN-junction formed adjacent to a front face of the device with electrodes formed on that face. The rear face of the photodiodes includes an opaque electrical contact.
Photodiodes having light responsive rear faces also have been made for a variety of applications, mostly military. Such devices have opaque surface layers on the front face precluding the possibility of light reaching that face. The rear face also includes electrodes. The devices are quadrature devices having four discrete sensor areas and are used, for example, for laser guided missile controls.
Deposited surface filters for photodiodes also are disclosed in U.S. Pat. No. 4,158,133 for front face wavelength adjustment of incident light. There is no showing of rear face filter usage or use of both front and rear face light response with or without filters on one of or both such faces.